The indexing system of the present invention may have application to many types of devices rotatable between two predetermined rotative positions. The indexing system is particularly well adapted for the control and actuation of the rotary work piece changer of a machining center. For purposes of an exemplary showing, the indexing system of the present invention will be described in terms of this application.
In a typical machining center, the work pieces to be machined are supported on work-holder pallets. The machining center has a work or machining zone and a load/unload zone. Upon completion of a machining operation, it is necessary to move the machined work piece from the machining zone to the load/unload zone, while at the same time moving an unmachined work piece from the load/unload zone to the machining zone. To accomplish this interchange, it is common practice to provide a rotary work changer for supporting and interchanging the work-holder pallets between the machining zone and the load/unload zone. It is desireable that the interchange be made as fast as possible and that the rotary work changer be characterized by uniform performance under different load conditions.
To accomplish this, the present invention teaches an indexing system which comprises a hydraulically powered actuator operatively connected to the rotary work changer of the machining center. The rotary actuator has first and second ports, either one of which may be connected to a hydraulic fluid pressure line, the other being connected to a hydraulic fluid return line, depending upon whether the rotary work changer is to be rotated in a clockwise or counterclockwise direction. A directional valve is provided to determine which of the first and second ports of the actuator is to be connected to the hydraulic pressure line, and which is to be connected to the hydraulic fluid return line. A control valve is interposed between the hydraulic actuator ports and the directional valve and controls the rate of rotation of the rotary work changer in direct response to the rotative position of the rotary work changer, all as will be described hereinafter. It has been found that the indexing system of the present invention is substantially insensitive to mass and temperature. The indexing system of the present invention can be built and tested as a separate unit and then mounted on the machine center.